DENVER (CN) - Colorado's plan to reduce Front Range air pollution wrongly exempted temporary emissions, the 10th Circuit concluded in an opinion published Monday, remanding the case to the Environmental Protection Agency for further proceedings.

Since 2008, Colorado has failed to meet federal standards for ground level ozone across the Denver Metro Nonattainment Area, which spans eight counties and is home to 3.3 million people.

In November 2022, the Center for Biological Diversity challenged the U.S. Environmental Protection Agency's approval of Colorado's state implementation plan to reduce harmful ground-level ozone, as measured by the National Ambient Air Quality Standards, because it wouldn't adequately regulate oil and gas activity.

The current plan only considers emissions produced during the operation of wells, leaving out the VOCs, or volatile organic compounds, emitted during drilling and fracking activities. Only tracking some emissions from oil and gas producers means operators will not be subjected to regulation as a major source of air pollution.

Ground-level ozone forms when sunlight reacts to nitrogen oxides and VOCs, which are produced by cars, power plants and industrial facilities. The resulting pollution can cause heart and lung disease as well as premature deaths and birth risks.

"The EPA acted contrary to law in allowing Colorado to exclude all temporary emissions under its permit program," wrote U.S. Circuit Judge Nancy Moritz in an 18-page opinion.

The Clean Air Act was clear, Moritz wrote, in regulating pollution based on source, not duration. Therefore, the EPA could not allow Colorado to sweepingly exempt temporary emissions.

"Had the EPA originally intended to exclude all temporary emissions under 51.165, it would have said so," Moritz added. "Having found no genuine ambiguity on this point, we do not defer to the EPA's interpretation."

At the same time, the panel affirmed Colorado's ability to "exclude emissions from internal combustion engines on any vehicle," and rejected the Center for Biological Diversity procedural challenge to the EPA's public comments process.

Biden-appointed U.S. Circuit Judge Veronica Rossman joined Moritz, an Obama-appointee, on the opinion.

U.S. Circuit Judge Timothy Tymkovich, appointed by George W. Bush, dissented from the majority in a 5-page opinion that said Colorado's temporary emissions rule legally differed from the Clean Air Act.

Tymkovich saw "temporary emissions" falling into a federal exemption to emissions "which would occur as a result of the construction or operation of a major stationary source."

Additionally, Tymkovich found Colorado's rule to be just as stringent as the federal rule, rendering it permissible.

Therefore Tymkovich would have rejected all of the Center for Biological Diversity arguments and let the EPA's approval of Colorado's state implementation plan stand.

In a footnote, he repeated an argument put forth by the American Petroleum Institute in an amicus brief: that other regulations adequately addressed emissions from oil and gas activities like drilling, fracking and flowback.

While the decision doesn't completely overhaul Colorado's implementation plan, the Center for Biological Diversity called it a "legal victory" leading the way for the organization to file similar challenges in Texas, New Mexico and Pennsylvania.

"Colorado can't keep permitting more oil and gas wells to spew pollution and pretend that it's working to fix our severe smog problem," said Robert Ukeiley, a senior attorney at the center, in a statement. "This decision will force the EPA and Colorado's Air Pollution Control Division to crack down on this dangerous pollution from dirty fossil fuels."

Ukeiley wrote that he hopes stricter regulation on oil and gas will help drive a transition to renewable energy.

U.S. attorneys who represented the government on appeal did not immediately respond to requests for comment.

Source: Courthouse News Service